The European carriers will be selling it starting in mid-2013. Manufacturers of the phones so far include Alcatel, LG and ZTE, Huawei.

U.S. users can get their hands on the OS by installing it on an Android phone. Plus, a company called Geeksphone makes the device.

The Verge's Chris Ziegler, who was living blogging today's press conference at the Mobile World Congress show in Barcelona, wasn't too impressed with the ZTE Open. He called it "an extremely low-end device."

Quality aside, this is an interesting experiment by Mozilla. This smartphone OS is built entirely from Web standards, like HTML5, and "free from the rules and restrictions of existing proprietary platforms," Mozilla says.